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Old 09-18-2020, 03:10 PM   #1
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Another lithium battery question.

I am in need of understanding the relationship between a standard alternator and a lithium battery with BMS. I read some articles about having to change the alternator when you swith to the lithium.
What is the downside of not changing but using the original alternator. 2005 8.1 engine.
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Old 09-18-2020, 03:41 PM   #2
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I am in need of understanding the relationship between a standard alternator and a lithium battery with BMS. I read some articles about having to change the alternator when you swith to the lithium.
What is the downside of not changing but using the original alternator. 2005 8.1 engine.
Trouble is most lithium batteries will take a 1C charge. So if you have 200 a/h's of lithium, might ask alternator to produce that, a problem if you have a smaller alternator.
You can change the alternator, but most just buy a DC-DC charger, this will take your normal start battery voltage from alternator and limit the charging current and supply the 14+ volts most lithium require to reach 100% SOC.
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Old 09-18-2020, 07:59 PM   #3
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My installation involved replacing the batteries, converter, and the BIM (may be a bird or called something else in your rig) The BIM (Battery isolation monitor) controls the connection between the house batteries and the chassis battery. Replacing the BIM (for me) prevented overtaxing the alternator by limiting the charge time (cycling on and off) in a manner to allow charging , but not burn up the alternator. Cheaper than a new alternator.



I put in 600w of solar too, but that is a different part of the equation.
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Old 09-18-2020, 09:50 PM   #4
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Yes, the BIM will work, tried a direct connection [like the BIM] between alternator and coach batteries before I went to dc-dc charger. Alternator case temp went from ambient to 250 F. in 5 minutes. Alternator will generally settle at 13.7 volts or there about, not enough to fully charge a lithium battery. Lithium BIM is cheaper, but will never bring your lithium batteries to 100% SOC. But agree that if you have solar, it can do the topping off charge.
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Old 09-19-2020, 05:46 AM   #5
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So this BMI, does it look like a relay with coach and chassis batteries connected to it?
And is it possible to just eliminate the connection between the two sets of batteries, realizing that the alternator would no longer charge the coach batteries.
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Old 09-19-2020, 09:15 AM   #6
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I have a TT. So it does not have a BIM. I want to charge thru the 7 pin trailer connector. About 10awg and fused for 30A in Tow Vehicle. Shuts off when engine is not running, so must have relay.
Anyway, don't want to go over 30A from TV. So looking at 20A max output.
Renogy Board 20A DC to DC Battery Charger Using Multi-stage Charging. ~ $120 Some Amazon reviews are bad. Has an ignition input to control turn on. But it is too voltage sensitive to work on 7 pin power. Some work around by connecting to running lights. I might use a small voltage boost board powered by 7 pin.
Victron has an 18A model I cannot find. Orion Tr-Smart are expensive and have Blue Tooth. Beware, they have DC-DC converters which are not chargers.
Other Brands and Inputs?
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Old 09-19-2020, 09:42 AM   #7
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Yes, the BIM will work, tried a direct connection [like the BIM] between alternator and coach batteries before I went to dc-dc charger. Alternator case temp went from ambient to 250 F. in 5 minutes. Alternator will generally settle at 13.7 volts or there about, not enough to fully charge a lithium battery. Lithium BIM is cheaper, but will never bring your lithium batteries to 100% SOC. But agree that if you have solar, it can do the topping off charge.
I have the same issue. When I've looked at dc-dc chargers I didn't think there was much difference in price so was thinking which ever was the easiest install. But your post makes me wonder. IIRC, I've seen dc-dc chargers at 20, 40 and 60 amps. My thought was it had to do with charging speed but I wasn't sure. How did you size your charger?
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Old 09-19-2020, 10:49 AM   #8
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I have the same issue. When I've looked at dc-dc chargers I didn't think there was much difference in price so was thinking which ever was the easiest install. But your post makes me wonder. IIRC, I've seen dc-dc chargers at 20, 40 and 60 amps. My thought was it had to do with charging speed but I wasn't sure. How did you size your charger?
I have pretty big solar, so I didn't need a big one, so I went with the Victron 30 amp model. It has an adjustable output, so set it to 14.4 constant voltage to suit my Battleborn's. I just use it to replace my isolator or BIM if you have one. Only drawback is that your coach batteries cannot charge your start batteries if you sit for any period of time. I just installed a 3 amp 120 volt 3 stage charger on my start batteries and plugged into inverter circuit for that scenario.

The bigger the dc-dc charger, the faster you can charge your house batteries, but personally would not go over half of your alternators rated output. Make sure your dc-dc charger has a output that matches your house battery requirements.

Pretty easy to install, one terminal to start battery/alternator, and the other terminal to your house batteries. The Victron I bought has a bluetooth output so I can set voltages etc and read charging rates on my phone.
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Old 09-23-2020, 05:45 PM   #9
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I have pretty big solar, so I didn't need a big one, so I went with the Victron 30 amp model. It has an adjustable output, so set it to 14.4 constant voltage to suit my Battleborn's. I just use it to replace my isolator or BIM if you have one. Only drawback is that your coach batteries cannot charge your start batteries if you sit for any period of time. I just installed a 3 amp 120 volt 3 stage charger on my start batteries and plugged into inverter circuit for that scenario.

The bigger the dc-dc charger, the faster you can charge your house batteries, but personally would not go over half of your alternators rated output. Make sure your dc-dc charger has a output that matches your house battery requirements.

Pretty easy to install, one terminal to start battery/alternator, and the other terminal to your house batteries. The Victron I bought has a bluetooth output so I can set voltages etc and read charging rates on my phone.
We have a similar set-up albeit ours is wired at 24V. We also went with the Victron Orion DC-DC smart charger, 2 actually wired in parallel putting out 30A @24V which when used in conjunction with our similar solar system allows us to run a single rooftop AC unit while underway and still have a small excess to also charge the batteries or alternately put a very big charge to the batteries when no need for rooftop AC in needed.
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Old 09-24-2020, 07:15 AM   #10
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We're running a Victron Orion 12/12-18 DC-DC charger on our trailer to charge two BattleBorn 100aH batteries. It charges at a little over 25A max and will charge our batteries back up pretty quick.

I ran a dedicated 4AWG charging circuit from one of our truck's batteries back to the charger, installed a manual disconnect switch and use the charger's engine detection system for start/stop of the charger.















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Old 09-25-2020, 03:43 PM   #11
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Nice set up,
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